- Email: [email protected]
The distribution and morphology of trace Mg at a grain boundary in a Ni-base superalloy
Scripta METALLURGICA
Vol. 23, pp. 1537-1542, 1989 Printed in the U.S.A.
Pergamon Press plc All rights reserved
THE DISTRIBUTION AND MORPHOLOGY OF TRACE Mg AT A GRAIN BOUNDARY IN A Ni-BASE SUPERALLOY
Jing Z h u ,
Z.Y. Cheng and H.Q. Yet
C e n t r a l Iron and Steel Research I n s t i t u t e , B e i j i n g 100081, China tLab. of Atomic Imaging of S o l i d s , Academia S i n i c a , Shenyang 110015
(Received April 25, 1989) (Revised June 20, 1989) INTRODUCTION It i s w e l l known t h a t the high temperature toughnesses of some s u p e r a l l o y s are improved by the a d d i t i o n of a t r a c e of Mg. Several proposals f o r the mechanism of the Mg e f f e c t are described elsewhere, such as s p h e r o i d i z a t i o n of carbides ( I - 2 ) , Mg s e g r e g a t i o n at the g r a i n boundary ( 3 ) , sulphur removal ( 4 ) , increase of the degree of long range o rd e r of the y ' phase c o n t a i n i n g Mg ( 56 ), e t c . In t h i s work the d i s t r i b u t i o n and morphology of Mg at a g r a i n boundary in a Ni-base s u p e r a l l o y c o n t a i n i n g d i f f e r e n t amounts of Mg have been i n v e s t i g a t e d by high s p a t i a l r e s o l u t i o n a n a l y t i c a l e l e c t r o n microscopy.
EXPERIMENTAL
PROCEDURES
Ni-e. [email protected] The nominal composition of GH220 i s -0.3U-0.020 ( w t . ~ ) . The a l l o y s A, B and C c o n t a i n 0.001, 0.005 and 0.019 Mg (wt.~), r e s p e c t i v e l y . Wrapped i n g o t s of the a l l o y s were forged t o discs by a h y d r o s t a t i c press, and then were h e a t - t r e a t e d as f o l l o w s : 1220°C x 4h + 1058°C x 4h + 958°C x 2h The mechanical p r o p e r t i e s of the a l l o y s a f t e r heat t r e a t m e n t are l i s t e d in Table I . Table I . Mechanical P r o p e r t i e s
Alloy
A B
C
950°C a (MPa) 559 565 586
Tension 8 5~ 5.2 16.0 12.0
test ~ 5~ 7.53 15.73 11.70
940°C, • (h) 25 >62 53
216 MPa 8 5~ ~ 5~ 2.40 9.28 3.20
This work was supported by China Nature Science Foundation
1537 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
3.17 9.44
2.70
1538
Mg IN Ni-BASE S U P E R A L L O Y
Vol.
23, No.
9
RESULTS AND DISCUSSION In t h i s s u p e r a l l o y , the i n t e r f a c e between a c a r b i d e a t a g r a i n boundary and one of its neighboring grains is semicoherent, but the interface between this carbide and the other neighboring grain is incoherent, These two interfaces are now considered s e p a r a t e l y . Figure I i s a l a t t i c e image of a semicoherent i n t e r f a c e between a c a r b i d e at g r a i n boundary and a y ' p a r t i c l e in the B - a l l o y specimen which had been creep r u p t u r e d ; the [110] zones of the c a r b i d e and the m a t r i x are p a r a l l e l to the e l e c t r o n beam. In Fig. 1 the two p a r t s of the c a r b i d e show two types of projection pattern. The i n s e r t e d e l e c t r o n d i f f r a c t i o n p a t t e r n i n d i c a t e s t h a t they are t w i n s , perhaps deformation t w i n s produced by d e f o r m a t i o n of the c a r b i d e d u r i n g creep t e s t i n g . Along the semi-coherent i n t e r f a c e the lattice arrangement m a i n t a i n s a good correspondence. More vacancies w i l l appear at an i n t e r f a c e when i t loses semi-coherence. Usually t h e r e i s a p r i s m a t i c - c o r n e r in the morphology of the c a r b i d e , for example, as in Fig. 2a. The schematic drawing of the lattice arrangement (Fig. 2b) of the carbide, marked in Fig. 2a, and the n e i g h b o r i n g y' indicates that l a t t i c e mismatching appears at the bend in the i n t e r f a c e of the c a r b i d e . F i g u r e 2c i s an e l e c t r o n m i c r o d i f f r a c t i o n p a t t e r n from the same mismatching area marked by a c i r c l e in Fig. 2b; i t was taken on a JEM-200¢FX e l e c t r o n microscope w i t h about a 20nm probe s i z e . F i g u r e 2d i s a schematic i n d e x i n g of Fig. 2c, which shows t h a t t h e r e are Ni2MQ n a n o c r y s t a l s at t h a t "mismatching" area. Due t o the probe b e a m convergence, s e v e r a l zones of the Ni2Mg e l e c t r o n d i f f r a c t i o n p a t t e r n a p p e a r on t h e n e g a t i v e s i m u l t a n e o u s l y . We now consider the i n c o h e r e n t i n t e r f a c e , in the B - a l l o y , w i t h the optimum p e r c e n t a g e o f Mg, t h e shapes o f t h e c a r b i d e s a t g r a i n b o u n d a r y is s m o o t h e r t h a n those in the s u p e r a l l o y w i t h o u t Mg. We f o u n d t h a t a s m a l l Ni-Mg phase i s wrapped up a r o u n d t h e t i p o f t h e c a r b i d e . F i g u r e 3a shows t h e m o r p h o l o g y o f a g r a i n boundary in the B - a l l o y , and t h e l o w e r r i g h t i n s e r t shows a shadow image o f t h e t o p o f t h e c a r b i d e i n d i c a t e d by t h e a r r o w . The dark c o n t r a s t p a r t i n t h e shadow image i s surrounded i n t e r m i n g l e d w i t h a grey c o n t r a s t p a r t . F i g u r e 3b and 3c are m i c r o d i f f r a c t i o n p a t t e r n s from the two p a r t s , r e s p e c t i v e l y . The a n a l y s i s of the m i c r o d i f f r a c t i o n p a t t e r n s shows t h a t the dark p a r t i s M6C, w h i l e the grey p a r t i s Ni2Mg. F i g u r e 4 i s a set of m i c r o d i f f r a c t i o n p a t t e r n s and the m i c r o a n a l y s i s from a c a r b i d e a t a g r a i n boundary in the creep r u p t u r e t e s t e d Calloy. Figure 4b and 4c a r e f r o m an i n c o h e r e n t b o u n d a r y (marked by a "U" in Fig. 4a). Figure 4c shows t h e e x i s t a n c e o f Mg and F i g . 4b shows t h e e x i s t a n c e o f the Ni2Mg p r e c i p i t a t i o n . By c o m p a r i s o n , F i g s . 4d and 4e f r o m a semicoherent b o u n d a r y (marked by a "D" i n F i g . 4a) show no o b s e r v a b l e Mg o r o t h e r compounds. Figure 5 i s a x-ray mapping - a map distribution of each element in the, Balloy, It shows t h a t the Ni and AI are the y ' - p h a s e elements; Co , Cr and a p a r t of Ni are the m a t r i x elements; w h i l e Mo, W and a p a r t of Cr are the c a r b i d e elements. In comparing the d i s t r i b u t i o n image of Mo (or W, or Cr) w i t h Mg i t can
Vol.
23, No. 9
Mg IN Ni-BASE
SUPERALLOY
1539
be seen t h a t Mg i s c o n c e n t r a t e d at the i n t e r f a c e between the c a r b i d e and y'phase (or m a t r i x ) , but only one side of the c a r b i d e (as i n d i c a t e d by the arrow in Fig.5). The x - r a y map (Fig. 5) was taken by Tracker Northen 5 5 8 0 system a t t a c h e d on JEM-2000FX,
SUMMARY I. The Mg i s c o n c e n t r a t e d around the g r a i n boundary, e s p e c i a l l y at the i n c o h e r e n t i n t e r f a c e between the c a r b i d e and the m a t r i x (or y ' - p h a s e ) t o form a small Laves phase Ni2Mg, which i s of about 20nm s i z e . This Laves phase makes the boundary r i c h in Mg, the f l a n k of the c a r b i d e smooth, the d e p l e t e d zone effectively s h r i n k and the d e n s i t y of vacancies at the g r a i n boundary decrease From Table 1 i t seems t h a t the small Laves phase Ni2Mg (about 10nm s i z e ) does not damage the d u c t i l i t y but does improve the high temperature creep f r a c t u r e toughness. 2. I t has never been r e p o r t e d b e f o r e t h a t any i n t e r m e t a l l i c Ni-Mg phase e x i s t s in a Ni-base s u p e r a l l o y w i t h a such low percentage ( 0 . 0 0 5 w t . ~ ) of Mg. The reason is t h a t the s p a t i a l r e s o l u t i o n i s so poor in c o n v e n t i o n a l e x p e r i m e n t a l methods, that the diffraction i n t e n s i t y and o t h e r i n f o r m a t i o n from the small Ni-Mg p a r t i c l e s are much less than what can be observed. However m i c r o d i f f r a c t i o n and m i c r o a n a l y s i s i s a p o t e n t i a l l y powerful t o o l f o r the i n v e s t i g a t i o n of the very f i n e scale m i c r o s t r u c t u r e . REFERENCES 1
KE Danian
and
ZHONG Zengyong,
ACTA M e t a l l u r g i c a
Sinica
(China),
3,
73
(1983). 2 3
Z . M .K a l e n i n a , e t a l , B u l l e t i n Academia S i n i c a USSR Metal, No.4 (1973) 193. ZHU Qiang et a l , , e d i t e d by Hsu Zhichao and Ma P e i l i , p.33, Chinese M e t a l l u r g i c a l Pub. Company (1987).
4 5 6
S.S. Chirnik, et al, Bulletin Academia Sinica USSR Metal, No.1(1973)144 HAN Linguang, Metal Science and Technology (China), 9ol.6, No.2, 83 (i987). LU Cuifen, MA Peili and ZHU Jing, "Magnesium Distribution in A Nickel-base Superalloy", unpublished.
1540
Mg IN Ni-BASE S U P E R A L L O Y
Vol.
23, No.
9
Y
Fig. 1 The l a t t i c e image of a semicoherent g r a i n boundary between a ¥' particle and a c a r b i d e i n t h e B a l l o y , w h i c h had been c r e e p r u p t u r e d . The M6C c a r b i d e shows two projection patterns, the analysis of the ~nserted d i f f r a c t i o n i n d i cates t h a t t h e y a r e t w i n s . The lattice arrangement at the semicoherent boundary maintains good continu'ity.
r ~/!~iiii/~¸¸~ ,
~i~!i¸i¸ii
Fig. 3 The image and m i c r o d i f f r a c t i o n s of a carbide at a grain boundary in a creep ruptured specimen of the B alloy. At the lower right of Fig. 3a the inserted shadow image of the top of a carbide, which is indicated by an arrow, shows that the top of the carbide is intermingled with N i 2 M g precipitates.
Vol.
23, No.
9
Mg IN Ni-BASE SUPERALLOY
1541
2a
@. . . . . . .
2d
,+ •
•
r'
!I I I
N~II
+I I I
Ni2Mq
llll I ~l
• Ni2Mq llh I h
~..-'.++.'
•
NiSMg
11 Z +[I
Ni~Nq it+ + +] @ NiZqq
i l l TTJ
Fig, 2
Ni2Mg p r e c i p i t a t e s at a corner of a carbide where the interface loses semicoherence. Figs. 2a and 2b. The morphology , SED p a t t e r n and the schematic drawing of the l a t t i c e arrangement of a semicoherent i n t e r f a c e between M@C and y ' , respect i v e l y . A vacancy appears at the mismatching area of the i n t e r f a c e . Figs. 2c and 2d. The m i c r o d i f f r a c t i o n p a t t e r n and shadow image from the mismatching area marked by a c i r c l e in Fig. 2b. Fig.2d is the i n d e x i n g of Fig. 2c; i t shows t h a t the Ni2M9 e x i s t s at the i n t e r f a c e ,
Fig. 5 X-ray mapping from the B - a l l o y . The arrow i n d i c a t e s a p o r t i o n of c o n c e n t r a t e d at one side of the i n t e r f a c e between the c a r b i d e and y ' - p h a s e .
Mg
1542
Mg IN Ni-BASE SUPERALLOY
Vol.
23, No. 9
i
U ~Aci~
J
II
.
ot
Q
Fig. 4 A set of m i c r o d i f f r a c t i o n p a t t e r n s and m i c r o a n a l y s i s from a c a r b i d e at a g r a i n boundary in the creep r u p t u r e d specimen of a l l o y C. Figs. 4c and 4b from an i n c o h e r e n t boundary (marked by a "U" in Fig. 4a) show the e x i s t e n c e of Mg and Ni 2Mg p r e c i p i t a t i o n . Figs. 4d and 4e from a semicoherent boundary ( marked by "D" in Fig. da) show no observable Mg or o t h e r compounds.
Vol. 23, pp. 1537-1542, 1989 Printed in the U.S.A.
Pergamon Press plc All rights reserved
THE DISTRIBUTION AND MORPHOLOGY OF TRACE Mg AT A GRAIN BOUNDARY IN A Ni-BASE SUPERALLOY
Jing Z h u ,
Z.Y. Cheng and H.Q. Yet
C e n t r a l Iron and Steel Research I n s t i t u t e , B e i j i n g 100081, China tLab. of Atomic Imaging of S o l i d s , Academia S i n i c a , Shenyang 110015
(Received April 25, 1989) (Revised June 20, 1989) INTRODUCTION It i s w e l l known t h a t the high temperature toughnesses of some s u p e r a l l o y s are improved by the a d d i t i o n of a t r a c e of Mg. Several proposals f o r the mechanism of the Mg e f f e c t are described elsewhere, such as s p h e r o i d i z a t i o n of carbides ( I - 2 ) , Mg s e g r e g a t i o n at the g r a i n boundary ( 3 ) , sulphur removal ( 4 ) , increase of the degree of long range o rd e r of the y ' phase c o n t a i n i n g Mg ( 56 ), e t c . In t h i s work the d i s t r i b u t i o n and morphology of Mg at a g r a i n boundary in a Ni-base s u p e r a l l o y c o n t a i n i n g d i f f e r e n t amounts of Mg have been i n v e s t i g a t e d by high s p a t i a l r e s o l u t i o n a n a l y t i c a l e l e c t r o n microscopy.
EXPERIMENTAL
PROCEDURES
Ni-e. [email protected] The nominal composition of GH220 i s -0.3U-0.020 ( w t . ~ ) . The a l l o y s A, B and C c o n t a i n 0.001, 0.005 and 0.019 Mg (wt.~), r e s p e c t i v e l y . Wrapped i n g o t s of the a l l o y s were forged t o discs by a h y d r o s t a t i c press, and then were h e a t - t r e a t e d as f o l l o w s : 1220°C x 4h + 1058°C x 4h + 958°C x 2h The mechanical p r o p e r t i e s of the a l l o y s a f t e r heat t r e a t m e n t are l i s t e d in Table I . Table I . Mechanical P r o p e r t i e s
Alloy
A B
C
950°C a (MPa) 559 565 586
Tension 8 5~ 5.2 16.0 12.0
test ~ 5~ 7.53 15.73 11.70
940°C, • (h) 25 >62 53
216 MPa 8 5~ ~ 5~ 2.40 9.28 3.20
This work was supported by China Nature Science Foundation
1537 0036-9748/89 $3.00 + .00 Copyright (c) 1989 Pergamon Press plc
3.17 9.44
2.70
1538
Mg IN Ni-BASE S U P E R A L L O Y
Vol.
23, No.
9
RESULTS AND DISCUSSION In t h i s s u p e r a l l o y , the i n t e r f a c e between a c a r b i d e a t a g r a i n boundary and one of its neighboring grains is semicoherent, but the interface between this carbide and the other neighboring grain is incoherent, These two interfaces are now considered s e p a r a t e l y . Figure I i s a l a t t i c e image of a semicoherent i n t e r f a c e between a c a r b i d e at g r a i n boundary and a y ' p a r t i c l e in the B - a l l o y specimen which had been creep r u p t u r e d ; the [110] zones of the c a r b i d e and the m a t r i x are p a r a l l e l to the e l e c t r o n beam. In Fig. 1 the two p a r t s of the c a r b i d e show two types of projection pattern. The i n s e r t e d e l e c t r o n d i f f r a c t i o n p a t t e r n i n d i c a t e s t h a t they are t w i n s , perhaps deformation t w i n s produced by d e f o r m a t i o n of the c a r b i d e d u r i n g creep t e s t i n g . Along the semi-coherent i n t e r f a c e the lattice arrangement m a i n t a i n s a good correspondence. More vacancies w i l l appear at an i n t e r f a c e when i t loses semi-coherence. Usually t h e r e i s a p r i s m a t i c - c o r n e r in the morphology of the c a r b i d e , for example, as in Fig. 2a. The schematic drawing of the lattice arrangement (Fig. 2b) of the carbide, marked in Fig. 2a, and the n e i g h b o r i n g y' indicates that l a t t i c e mismatching appears at the bend in the i n t e r f a c e of the c a r b i d e . F i g u r e 2c i s an e l e c t r o n m i c r o d i f f r a c t i o n p a t t e r n from the same mismatching area marked by a c i r c l e in Fig. 2b; i t was taken on a JEM-200¢FX e l e c t r o n microscope w i t h about a 20nm probe s i z e . F i g u r e 2d i s a schematic i n d e x i n g of Fig. 2c, which shows t h a t t h e r e are Ni2MQ n a n o c r y s t a l s at t h a t "mismatching" area. Due t o the probe b e a m convergence, s e v e r a l zones of the Ni2Mg e l e c t r o n d i f f r a c t i o n p a t t e r n a p p e a r on t h e n e g a t i v e s i m u l t a n e o u s l y . We now consider the i n c o h e r e n t i n t e r f a c e , in the B - a l l o y , w i t h the optimum p e r c e n t a g e o f Mg, t h e shapes o f t h e c a r b i d e s a t g r a i n b o u n d a r y is s m o o t h e r t h a n those in the s u p e r a l l o y w i t h o u t Mg. We f o u n d t h a t a s m a l l Ni-Mg phase i s wrapped up a r o u n d t h e t i p o f t h e c a r b i d e . F i g u r e 3a shows t h e m o r p h o l o g y o f a g r a i n boundary in the B - a l l o y , and t h e l o w e r r i g h t i n s e r t shows a shadow image o f t h e t o p o f t h e c a r b i d e i n d i c a t e d by t h e a r r o w . The dark c o n t r a s t p a r t i n t h e shadow image i s surrounded i n t e r m i n g l e d w i t h a grey c o n t r a s t p a r t . F i g u r e 3b and 3c are m i c r o d i f f r a c t i o n p a t t e r n s from the two p a r t s , r e s p e c t i v e l y . The a n a l y s i s of the m i c r o d i f f r a c t i o n p a t t e r n s shows t h a t the dark p a r t i s M6C, w h i l e the grey p a r t i s Ni2Mg. F i g u r e 4 i s a set of m i c r o d i f f r a c t i o n p a t t e r n s and the m i c r o a n a l y s i s from a c a r b i d e a t a g r a i n boundary in the creep r u p t u r e t e s t e d Calloy. Figure 4b and 4c a r e f r o m an i n c o h e r e n t b o u n d a r y (marked by a "U" in Fig. 4a). Figure 4c shows t h e e x i s t a n c e o f Mg and F i g . 4b shows t h e e x i s t a n c e o f the Ni2Mg p r e c i p i t a t i o n . By c o m p a r i s o n , F i g s . 4d and 4e f r o m a semicoherent b o u n d a r y (marked by a "D" i n F i g . 4a) show no o b s e r v a b l e Mg o r o t h e r compounds. Figure 5 i s a x-ray mapping - a map distribution of each element in the, Balloy, It shows t h a t the Ni and AI are the y ' - p h a s e elements; Co , Cr and a p a r t of Ni are the m a t r i x elements; w h i l e Mo, W and a p a r t of Cr are the c a r b i d e elements. In comparing the d i s t r i b u t i o n image of Mo (or W, or Cr) w i t h Mg i t can
Vol.
23, No. 9
Mg IN Ni-BASE
SUPERALLOY
1539
be seen t h a t Mg i s c o n c e n t r a t e d at the i n t e r f a c e between the c a r b i d e and y'phase (or m a t r i x ) , but only one side of the c a r b i d e (as i n d i c a t e d by the arrow in Fig.5). The x - r a y map (Fig. 5) was taken by Tracker Northen 5 5 8 0 system a t t a c h e d on JEM-2000FX,
SUMMARY I. The Mg i s c o n c e n t r a t e d around the g r a i n boundary, e s p e c i a l l y at the i n c o h e r e n t i n t e r f a c e between the c a r b i d e and the m a t r i x (or y ' - p h a s e ) t o form a small Laves phase Ni2Mg, which i s of about 20nm s i z e . This Laves phase makes the boundary r i c h in Mg, the f l a n k of the c a r b i d e smooth, the d e p l e t e d zone effectively s h r i n k and the d e n s i t y of vacancies at the g r a i n boundary decrease From Table 1 i t seems t h a t the small Laves phase Ni2Mg (about 10nm s i z e ) does not damage the d u c t i l i t y but does improve the high temperature creep f r a c t u r e toughness. 2. I t has never been r e p o r t e d b e f o r e t h a t any i n t e r m e t a l l i c Ni-Mg phase e x i s t s in a Ni-base s u p e r a l l o y w i t h a such low percentage ( 0 . 0 0 5 w t . ~ ) of Mg. The reason is t h a t the s p a t i a l r e s o l u t i o n i s so poor in c o n v e n t i o n a l e x p e r i m e n t a l methods, that the diffraction i n t e n s i t y and o t h e r i n f o r m a t i o n from the small Ni-Mg p a r t i c l e s are much less than what can be observed. However m i c r o d i f f r a c t i o n and m i c r o a n a l y s i s i s a p o t e n t i a l l y powerful t o o l f o r the i n v e s t i g a t i o n of the very f i n e scale m i c r o s t r u c t u r e . REFERENCES 1
KE Danian
and
ZHONG Zengyong,
ACTA M e t a l l u r g i c a
Sinica
(China),
3,
73
(1983). 2 3
Z . M .K a l e n i n a , e t a l , B u l l e t i n Academia S i n i c a USSR Metal, No.4 (1973) 193. ZHU Qiang et a l ,
4 5 6
S.S. Chirnik, et al, Bulletin Academia Sinica USSR Metal, No.1(1973)144 HAN Linguang, Metal Science and Technology (China), 9ol.6, No.2, 83 (i987). LU Cuifen, MA Peili and ZHU Jing, "Magnesium Distribution in A Nickel-base Superalloy", unpublished.
1540
Mg IN Ni-BASE S U P E R A L L O Y
Vol.
23, No.
9
Y
Fig. 1 The l a t t i c e image of a semicoherent g r a i n boundary between a ¥' particle and a c a r b i d e i n t h e B a l l o y , w h i c h had been c r e e p r u p t u r e d . The M6C c a r b i d e shows two projection patterns, the analysis of the ~nserted d i f f r a c t i o n i n d i cates t h a t t h e y a r e t w i n s . The lattice arrangement at the semicoherent boundary maintains good continu'ity.
r ~/!~iiii/~¸¸~ ,
~i~!i¸i¸ii
Fig. 3 The image and m i c r o d i f f r a c t i o n s of a carbide at a grain boundary in a creep ruptured specimen of the B alloy. At the lower right of Fig. 3a the inserted shadow image of the top of a carbide, which is indicated by an arrow, shows that the top of the carbide is intermingled with N i 2 M g precipitates.
Vol.
23, No.
9
Mg IN Ni-BASE SUPERALLOY
1541
2a
@. . . . . . .
2d
,+ •
•
r'
!I I I
N~II
+I I I
Ni2Mq
llll I ~l
• Ni2Mq llh I h
~..-'.++.'
•
NiSMg
11 Z +[I
Ni~Nq it+ + +] @ NiZqq
i l l TTJ
Fig, 2
Ni2Mg p r e c i p i t a t e s at a corner of a carbide where the interface loses semicoherence. Figs. 2a and 2b. The morphology , SED p a t t e r n and the schematic drawing of the l a t t i c e arrangement of a semicoherent i n t e r f a c e between M@C and y ' , respect i v e l y . A vacancy appears at the mismatching area of the i n t e r f a c e . Figs. 2c and 2d. The m i c r o d i f f r a c t i o n p a t t e r n and shadow image from the mismatching area marked by a c i r c l e in Fig. 2b. Fig.2d is the i n d e x i n g of Fig. 2c; i t shows t h a t the Ni2M9 e x i s t s at the i n t e r f a c e ,
Fig. 5 X-ray mapping from the B - a l l o y . The arrow i n d i c a t e s a p o r t i o n of c o n c e n t r a t e d at one side of the i n t e r f a c e between the c a r b i d e and y ' - p h a s e .
Mg
1542
Mg IN Ni-BASE SUPERALLOY
Vol.
23, No. 9
i
U ~Aci~
J
II
.
ot
Q
Fig. 4 A set of m i c r o d i f f r a c t i o n p a t t e r n s and m i c r o a n a l y s i s from a c a r b i d e at a g r a i n boundary in the creep r u p t u r e d specimen of a l l o y C. Figs. 4c and 4b from an i n c o h e r e n t boundary (marked by a "U" in Fig. 4a) show the e x i s t e n c e of Mg and Ni 2Mg p r e c i p i t a t i o n . Figs. 4d and 4e from a semicoherent boundary ( marked by "D" in Fig. da) show no observable Mg or o t h e r compounds.